1. Field of the Invention
This invention relates to a PVC-free multilayer tube for medical purposes according to the pre-characterising clause of claim 1, to a process for the production of such PVC-free multilayer tubes according to the pre-characterising clause of claim 18 and to the use of the PVC-free multilayer films according to the invention.
2. Description of the Prior Art
The following have been cited as prior art
WO-A-92/11820 (=D1), PA1 DE-A-28 31 034 (=D2), PA1 U.S. Pat. No. 4,948,643 (=D3), PA1 EP-A-0 136 848 (=D4), PA1 DE-PS-44 04 041 (=D5), PA1 DE-OS-42 19 071 (=D6), PA1 DE-OS-39 14 998 (=D7) and PA1 WO-A-93/23093 (=D8).
PVC-free materials=non-PVC materials and single-layer tubes produced therefrom having only one layer are known, for example, from D1. This document proposes a tube material for medical purposes which contains a blend of polyurethane and polyester and which may be subjected to sterilisation in an autoclave, is heat-sealable and is sealable and fusible with high frequency energy. The described tube material is free of the PVC plasticiser DEHP, a phthalate which is suspected of having carcinogenic characteristics. It does, however, optionally contain as plasticiser certain additional amounts of a citric acid ester (butyryltrihexyl citrate) and further processing auxiliaries such as internal or external lubricants. While the thermoplastic plastic material disclosed in D1 may be processed by known shaping processes such as extrusion, injection moulding or blow moulding, it is essentially intended for use in medical bags or connectors made from PVC. It is only with these "conventional" PVC materials that it exhibits satisfactory compatibility, in particular for joining by heat or high frequency sealing.
D2 discloses PVC-free plastic compositions which are suitable for the production of tubes to receive or convey blood or medical solutions. D2 in particular provides plastic compositions which consist of 10 to 40 wt. % of a polyolefin substantially consisting of propylene units, 40 to 85 wt. % of a block copolymer prepared from a central polyethylene or polybutylene block with terminal polystyrene blocks, 10 to 40 wt. % of a polymeric plasticiser based on polyethylene and optionally an anti-oxidant. While the materials disclosed are indeed flexible, thoroughly heat resistant, have the softness required for medical applications and are very largely capable of solving the ageing problems caused by low molecular weight plasticisers, the stability and stiffness of the material still leaves something to be desired. In the stated single-layer material, any increase in stiffness by increasing the proportion of polypropylene would in particular result in a reduction in the softness and flexibility of the finished tube or bag.
D3 provides multilayer tubes for medical connection lines. Three-layer tubes are shown, the outer layer of which is based on ethylene vinyl acetate (EVA) and the inner layer on polyvinyl chloride (PVC). Since adhesion between the inner and outer layers is deficient, a coupling agent layer made from an ethylene-based polymer containing vinyl acetates and acrylates, is coextruded with the other two materials as a central layer. Plastic materials having the stated sequence of layers are in particular suitable for use as junction and connection pieces or tubes for medical bags made from EVA (compatibility of the outer layer with the bag) and allow a PVC membrane tube to be introduced and securely attached within the junction piece or tube, for example by solvent bonding. The multilayer tubes shown in D3 are highly questionable from a medical point of view as the PVC layer contains considerable quantities of trimellitic acid esters as the plasticiser and these compounds may be carcinogenic.
D4 finally discloses multilayer tubes which may be considered as a potential replacement for PVC tubes in the medical sector. However, D4 does not completely exclude the use of PVC, indeed it is entirely tolerated as a material or blend component for an interlayer or the inner layer.
D4 specifically relates to a three-layer tube for medical purposes, the inner layer of which consists of an ethylene/propylene copolymer, a polypropylene, a copolyester prepared from a polyether and a polyethylene terephthalate, polyurethane, polyvinyl chloride or a blend of copolyester and ethylene/vinyl acetate copolymer.
The interlayer may consist of LLDPE (linear low density polyethylene), ethylene/vinyl acetate copolymer (EVAC), modified EVAC, ethylene/methyl acrylate copolymer (EMAC), modified EMAC, PVC or a blend of the above-stated compounds.
The outer layer according to D4 is formed from polypropylene, ethylene/propylene copolymer or modified ethylene/propylene copolymer.
Selection of the materials for the interlayer is substantially determined by the ability of these materials to impart the necessary flexibility to the complete multilayer tube structure. The criterion for selection of the inner layer material is sufficient heat resistance to render the resultant tube autoclavable, while selection of an outer layer material is substantially guided by the desire to allow relatively resistant ultrasound, heat or high frequency energy sealing with a polycarbonate connector.
Apart from the fact that the tubes according to D4 do not completely exclude the use of PVC, and while the tubes are indeed compatible with polycarbonate, they are less suited to forming a bond with other newer and more advantageous polypropylene-based bag or connector materials.
Moreover, the flexible central layer according to D4 is usually the thickest layer, which often entails inadequate stiffness of the complete tube. It is thus generally and not only optionally necessary to irradiate the extruded tubes in order to achieve high temperature sterilisability by means of radiation-induced crosslinking. This operation is elaborate.
D5 relates to a polymer material for medical instruments. Silane-grafted VLDPE's or ULDPE's are disclosed which have been crosslinked with moisture in order to obtain, for example, transparent, kink-resistant and sterilisable tubes, in particular by extrusion. Elevated degrees of crosslinking are a prerequisite for steam sterilisability of the finished product. Although the material is apparently suitable as a replacement for PVC, the resultant single-layer tubes are not capable forming a good and direct bond with an insert during simple high temperature sterilisation without losing dimensional stability.
D6 discloses radiation-sterilisable recyclable infusion and transfusion sets, in which all the components are produced from thermoplastic or elastomeric homopolymers, copolymers, block copolymers based on polyolefins. D6 in particular publically discloses connection tubes made from PE-LLD or from linear PE-LVLD, but does not exclude the use of EVA or special ionomers.
These tubes are connected by using organic solvents such as cyclohexane. Alternatively, the tubes may be welded by ultrasound or bonded with light- or UV-curable adhesives.
D7 relates to transfer systems for infusion of transfusion purposes, in which, in order to ensure environmentally sensitive recycling, all components consist of a single polymer, copolymer or block copolymer without using PVC. The polymeric materials used are based on styrene polymers.
D8 relates to PVC-free coextruded multilayer tubes for medical purposes which have a core layer consisting of a blend of polyamide and EVA. An outer layer is applied onto this inner core layer by means of a coupling layer. The coupling layer essentially contains copolyester and SEBS copolymer, optionally PP and EVA. Selection of the materials proves that the disclosed tube must have the disadvantages associated with the use of EVA, copolyester or polyamide.